1221257 - When scrolling off bottom of document, overscroll animation has a weird "jump", and/or there's a flicker of mis-scrolled content

Status: RESOLVED WORKSFORME

(Firefox for Android Graveyard :: Toolbar, defect)

Description

[Daniel Holbert [:dholbert]]

STR:
 1. Visit a long page, like e.g. this Alice in Wonderland text:
     https://www.gutenberg.org/files/11/11-h/11-h.htm
   (It might not even have to be that long; not sure)

 2. Scroll to near the bottom.

 3. Rapidly try to scroll off the bottom.

 (4. Repeat steps 2-3.)

ACTUAL RESULTS:
- The overscroll "gray halo" effect at the bottom of the screen sometimes has a weird discontinuous "jump". This looks a bit like it plays twice, but from inspecting a screencast, it looks like really there's a hump that rises smoothly and then falls smoothly, and while it's falling it suddenly jumps up to a much higher "peak" for a frame or two.

- There's often a flicker of the content at a mis-scrolled position.

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: screencast #1 of bug

Comment 2

[Daniel Holbert [:dholbert]]

I'm seeing this with latest Nightly 45 & Aurora 44, but I couldn't reproduce with Firefox Beta 42.  (Beta 43 hasn't come out yet.)

So, this might be a regression that we're shipping through the trains, or it might be triggered by some feature that's only enabled on Nightly/Aurora channels.

Comment 3

[Daniel Holbert [:dholbert]]

Attachment: screenshot of overscroll "hump" in wrong position, hovering many pixels away from the bottom of the screen

Here's a screenshot taken from the just-attached screencast (at about 5 seconds), showing the "hump" in the wrong position.

Comment 4

[Daniel Holbert [:dholbert]]

Attachment: screenshot of overscroll "hump" in correct position (taken just after prev. screenshot)

Here's a screenshot showing the correct position of the hump, taken just after the previous screenshot. (again, from my attached screencast)

Comment 5

[Daniel Holbert [:dholbert]]

I suspect the weird jump / offset-from-the-bottom might have to do with the URL bar reappearing (and stealing a chunk of the viewport) when you hit the bottom of the page.  The offset shown in the screenshot (attachment 8682667 [details]) does seem to be about the same size as the URL bar, at least.

Comment 6

[Kartikaya Gupta (email:[e-mail])]

Yeah this is probably a regression from bug 1180295. I've been seeing similar glitchiness but it's really hard to pin down. If you have reliable STR that would be super helpful.

Comment 7

[Daniel Holbert [:dholbert]]

STR in comment 0 are like 30-50% reliable.  (If I perform them a few times in a row, I'm pretty much bound to see glitchiness on one of the tries.)

Comment 8

[Daniel Holbert [:dholbert]]

(Regression-bug suspicion from comment 6 is consistent with versions-affected in comment 2, and also suggests that we're about to ship this bug in 43 beta, when that goes out.)

Comment 9

[Kartikaya Gupta (email:[e-mail])]

I'll see if I can pin this down.

Comment 10

[Kevin Brosnan [Ex-Mozilla]]

[Tracking Requested - why for this release]: regression

Comment 11

[Daniel Holbert [:dholbert]]

(RE regressionwindow-wanted -- sounds like Kats already has a good guess at what caused this, per comment 6. But it may be worthwhile to confirm his suspicion.)

Comment 12

[Ritu Kothari (:ritu) (Inactive, please n-i to RyanVM, jcristau, or pascal)]

Tracked for FF44+. FWIW, I was unable to see repro this issue using STR provided on DevEd44 build id: 20151125004042 on win8.

Comment 13

[Kartikaya Gupta (email:[e-mail])]

This is android-only. Also with the C++APZ enabled the overscroll effect will be disabled so as of today this probably won't be noticeable on the nightly channel.

Comment 14

[Ritu Kothari (:ritu) (Inactive, please n-i to RyanVM, jcristau, or pascal)]

Given that we don't have a fix yet and this does not seem to be release-blocking, marking this as wontfix for FF44. Please let me know if there are any concerns.

Comment 15

[Sylvestre Ledru [:Sylvestre]]

Not tracking anymore as it doesn't seem to be a big issue after all.

Comment 16

[Daniel Holbert [:dholbert]]

I'm actually not seeing the overscroll animation at all anymore, in latest Nightly on Android. It seems to have been removed.

Hence, resolving as WORKSFORME.

Comment 17

[Kartikaya Gupta (email:[e-mail])]

Yeah, with the C++ APZ enabled we don't have support for the overscroll animation. Aurora and up will still have this bug until APZ rides the trains on Fennec.